[terraform-plan] Add output for the plan file

[donovanmuller]

In context of using analysis tools like Checkov to scan Terraform plan files, is it possible to add new outputs to the terraform-plan action with the plan file contents.

Ideally in both default and JSON formats (JSON format required for Checkov).

[dflook]

v1.16.0 has just been released which has two new outputs:

• json_plan_path is a path to the generated plan in a JSON format file
• text_plan_path is a path to the generated plan in a human readable text file